The first place among Lincolnshire mines must be given to Scunthorpe and Frodingham in the north of the county. The fact that the ironstone there was sufficiently rich to make it worth smelting was only realised about the year 1855, when the late Lord St Oswald (then Mr Rowland Winn) first opened quarries. The ore was at that time taken to the river Trent, and shipped to iron-works in Yorkshire. The first blast furnace in the district was erected about 1864, and others followed shortly afterwards. There are now five firms who smelt iron on the spot, and in addition to the ore used by them, a very large quantity is sent to iron-works in Yorkshire and Derbyshire. The area in which ironstone is being dug extends from Ashby on the south to Thealby on the north, a distance of about seven miles its widest part measuring about a mile and a half and it includes portions of the parishes of Ashby, Brumby, Frodingham, Scunthorpe, Flixborough, Normanby, and Burton. The ore is a fossil-bearing limestone in the Lower Lias and contains the iron in the form of hydrated peroxide. The bed, where it attains its full thickness, is about 30 feet deep ; it has a slight north-easterly dip, and the quarries are all situated on its outcrop, so that the available thick- ness diminishes from east to west, according to the degree of denudation to which it has been subject. Towards the east the bed dips under the scarp of the hill ; but it was reached in shafts and borings near Appleby station at a depth of 300 feet, still being nearly 30 feet thick. The stone is all got in open quarries. It is covered with blown sand varying in depth from a few inches to about 30 feet, containing in places beds of peat. This is removed by digging and burrowing, or in some cases by mechanical means. The ironstone is got by drilling and blasting. The percentage of metallic iron varies in the different bands that make up the full thickness of the bed ; some of the richest yield upwards of 30 per cent, and some are too poor to treat. It has been calculated that on an average two tons of coal produce one ton of metal. The stone contains in itself sufficient lime to act as a flux, and a siliceous component is furnished by the ironstone of the Northampton Sands, quarried at Greetwell by Lincoln. The ore is smelted in large blast furnaces, and the result is mostly disposed of in the form of pig iron. But, a few years ago, one firm at Frodingham built steel works and rolling mills, using the Siemens-Martin method. The Lincolnshire steel is of very high quality, suitable for rolling into thin sheets or drawing into wire. Some extensive new works wherein both iron and steel will be made are nearing completion at Flixborough.

At Caythorpe are considerable open workings of the Middle Lias (Marlstone) ironstone.

At Greetwell and Monks Abbey, just east of Lincoln, as already mentioned, is quarried the siliceous ironstone found in the lowest layer of the Lower Oolite, known as the Northampton Sands. The ironstone is worked partly in the open when there is little soil above, but chiefly by galleries driven into the Cliff, with narrow-gauge rails and trucks, on which horse-traction is being superseded by small locomotives. The ore is reddish brown at the outcrop and gets bluer in colour the deeper the tunnel goes in. The yield of metal is from 28 to 40 per cent. The soil is replaced in the open workings, and has been covered with allotments, etc. ; in the other workings the galleries have fallen in and produced a very irregular surface.

Near Claxby and Nettleton the Middle Neocomian layer of ironstone, about six feet six inches thick, has been worked by galleries driven into the side of the hill. The workings began in 1868. The ore is almost entirely made up of small and beautifully polished oolitic grains of hydrated peroxide of iron. It is a calcareous ore, yielding from 28 to 33 per cent, of metallic iron, and is useful for mixing with the clayey ores of the coal- measures. From the presence of slag with charcoal and bits of pottery it is evident that this bed of ore was known to and worked by the Romans during their possession of this country.

The county is not rich in other minerals, coal not yet having been tapped to any practical result. The chief building stone is the Lincolnshire Limestone, an oolitic rock worked near Ancaster and Wilsford, at Haydor, and near Grantham, of which many churches and houses in Kesteven are built, including Lincoln Minster. It hardens on exposure and forms a most excellent building stone. Many churches on the Wolds and in the Marsh are built of the beautiful local grey-green sandstone (of the Lower Neocomian series), which unfortunately is rather perish- able. In some instances the white chalk is used for building, as at Legbourne Church, where the smooth white surface suggests at a distance unglazed white tiles. The clay on Lincoln hill and below the Cliff is extensively used for brick-making, and at Little Bytham are works for making so-called "clinker" bricks, which are specially hard and used as fire-bricks.